Electrical discharge device



April 26, 1938. 1.. K. MARSHALL ELECTRICAL DISCHARGE DEVICE OriginalFiled April 14, 1932 2 Sheets-Sheet l April 1938- 1 K. MARSHALLELECTRICAL DISCHARGE DEVICE Original Filed April 14, 1932 2 Sheets-Sheet2 Patented Apr. 26, 1938 UNITED STATES PATENT OFFICE or. by mesncassignments, to Raytheon Manufacturing Company, Newton, Mass, atcorporation of Deiaware Application April 14,

1932, Serial No. 605,249

Renewed July 13, 1937 36 Claims.

This invention relates to electrical discharge devices, and moreparticularly to full-wave rectifiers of the gaseous discharge type.

One of the objects of my invention is to produce such a device which iscapable of handling large values of current, power and voltage in aglass container.

Another object of my invention is to provide two anodes cooperating witha single cathode in a device of this kind, and to avoid the difficultieswhich the use of such two anodes involves in a simple and efficientmanner.

Another object of my invention is to produce all of the above resultswith very low losses, low voltage drop, and high efliciency.

A still further object of my invention is to design a structure for sucha device'which is particularly simple and rugged.

The foregoing and other objects of my invention will be best understoodfrom the following description of an exemplification thereof, referencebeing had to the accompanying drawings, wherein:

Fig. 1 is a vertical cross-sectional view of a full-wave rectifier,illustrating one embodiment of my invention;

Fig. 2 is a cross-sectional view taken along line 22 of Fig. 1;

Fig. 3 is a cross-sectional view of one of the anodes taken along line3-3 of Fig. 1;

Fig. 4 is a bottom view of the cathode taken along line 44 of Fig. 1;and

Fig. 5 is a diagrammatic view of a circuit which may be used with therectifier shown in Fig. 1.

The production of a gaseous discharge device of high power rating andefficiency involves various difficulties which must be met before such adevice can be considered suitable for modern commercial purposes.

First of all, in such a device, a cathode must be provided which, forlong periods and at low voltage drop, furnishes such a copious supply ofelectrons that currents of arc intensities may readily be drawntherefrom.

Secondly, the drop from the tube in the conducting direction must be aslow as can possibly be produced in order not only that the efficiencyshall be high but also so that the heat losses in the device shall notrise above a value which can satisfactorily be dissipated withoutelaborate cooling means.

Thirdly, when such devices are to be used as rectifiers, they must beable to withstand comparatively high reverse voltages impressedbetweenthe anode and the cathode.

High power discharge devices have heretofore been constructed in metalcontainers. This is the fourth difficulty which I have eliminated in mydevice. It is desirable to use glass as the envelope to contain suchdevices.

Fifth, it is desirable to devise means for keeping the vapor pressurewithin the device from rising to an excessive value.

The sixth problem is that of a sufficiently rugged construction so thatexcessive mechanical strains shall not appear in the device, eitherduring use or transportation. By utilizing devices constructed inaccordance with my invention, each of the above problems are solved.

The above features will be more readily understood by referring to thedrawings wherein an envelope I of refractory insulating material, suchas glass, encloses the cathode structure 2 and two anodes 3 and 4. Theenvelope l is approximately circular in cross-section, as shown in Fig.2, and is considerably longer than it is wide, as shown in Fig. 1. Theupper end of the container I is provided with a tubular neck 5 having areentrant stem 6. This reentrant stem has a lower wall 1. A heavyconducting rod 8, preferably of tungsten, serves as the main cathodelead and is sealed through the wall I by a seal 9, preferably of thetype as described in the patent of James D. LeVan, No. 2,057,661. Theupper end of the rod 8 is provided with a stranded copper conductor l0through which connections to an external circuit may be made. The rod 8extends from the upper end of the glass container l to a point adjacentthe bottom thereof, and at its lower end serves as the main support forthe cathode structure 2. This cathode structure consists primarily of ahollow tubular member ll provided with a series of external radial finsl2. The lower end of member II is closed by a cap I3. To the upper endof member II is welded a tubular extension M. The walls of this tubularextension may be considerably thinner than the walls of the member II.This tubular member II is formed by a strip of metal, which is foldedback on itself to form the tubular member II at the central portionthereof, as shown most clearly in Fig. 4. At one side of the tubularmember, the two sides of this strip are riveted together to provide aradial supporting arm l5. At the outer end of this supporting arm, thetwo sides of the strip are formed to provide a tubular clamping section16. The outer ends I! and I8 of the strip are flattened and disposedparallel to each other, and are also provided with a series of holesthrough which clamping bolts l9 pass. The lower end of the rod 8 isinserted in the clamping section II, and the cathode structure issecurely clamped thereto by means of the clamping bolts I. A tubularshield 28 surrounds the member II and the radiating fins l2, and isformed of a thin strip of metal riveted at its outer edges to the radialsupporting arm IS. The space between the upper end of the shield 20 andthe tubular member II is closed by an annular cap 2|. A heating filament22, preferably of tungsten, is supported within the hollow member II byan insulating plug 23 closing the upper end of the tubular extension l4.This heating filament 22 consists of a double helix, the two ends 24 and25 of which project through the insulating plug 23. Two lead-inconductors 2i and 21, which are preferably of tungsten, are also sealedthrough the wall I of the reentrant stem 8. Two intermediate conductors28 and 29, which are preferably of molybdenum or nickel, are provided toconnect the lead-in wires 26 and 21 to the ends 24 and 25 of the heatingfilament 22. The outer ends of each of the lead-in wires 28 and 21 arealso provided with stranded copper conductors 38 and 3| in order thatelectrical connection may be made with the external circuit. The entirecathode structure below the insulating plug 23 is constructed preferablyof tantalum. The external surface of the tubular member H and theradiating temperature. The coating which I prefer to use consists of amixture of the oxides-of barium,

calcium, potassium, sodium and thorium. This coating may be formed byapplying a coating of the nitrates of the above materials, and thenheating the surfaces in the presence of air to a temperature sufficientto oxidize the nitrates. I have found that such a cathode surface iscapable of withstanding discharges of arc intensities for very longperiods without any substantial impairment of such surface. At the endof the tubular member near the cap i3 is pro,- vided a series ofapertures 32 which enable electrons emitted from the filament to passout into, the external discharge space for the purpose of aiding in thestarting of the discharge. The shield 20, together with the annular cap2 I, forms a hollow cathode chamber within which the vapor pressure isto be maintained at a higher value than the pressure outside of saidcathode, in accordance with the invention set forth in the patent ofCharles G. Smith, No. 1,929,122.

It will be noted that the active portion of the cathode is located asremotely as possible from the seals through which the cathode lead 8 andheater leads 26 and 21 pass. Also the opening in the cathode from whichthe discharge 'is initiated is directed away from the stem 8 in whichsaid lead-in conductors are sealed. The bombardment of lead-in seals byions generated in a gaseous discharge has been a serious problem even indevices of moderate power. Such continued bombardment has often resultedin the destruction of the seal. In devices of high power and voltage,the problem becomes even more acute. It will be seen, however, that thelocation and spacing of the cathode with respect to its lead-in sealsare such as to effectively eliminate all such bombardment of theseseals. This spacing also eliminates the problem of excessive heating ofthe seals. Practically the only way in which heat can reach these sealsis along the conductors 8, 28 and 29. Since 28 and 23 are comparativelysmall, they will not conduct a sufficient amount of heat to injure theseals. Conductor 8 being much larger will conduct a larger amount ofheat. Also, substantially the entire load current is carried byconductor 8. This current is so large that a substantial amount of heatis generated thereby in said conductor. In order to get rid of this heatbefore it reaches the seal 9, conductor 8 is provided with an externalsleeve of a material which is a good heat radiator, such as, forexample, carbon. This sleeve also increases the total heat radiatingsurface of the conductor 8, and thus most of the heat carried by andgenerated in said conductor is radiated out into the gaseous filling ofthe tube and through to the walls of the tube before it reaches the seal8. In previous devices of this type under very heavy loads, failure hasoccured due to the discharge localizing on a portion of the cathodelead-in structure, and causing it to burn out. It will be noted that allof the metal parts connected to the cathode and exposed to the gaseousdischarge space are made of refractory metals which can withstand hightemperatures without burning out. Thus if such a discharge takes placeon said metal parts, they will not burn out. The provision of the sleeve8a also tends to prevent such a localization of the discharge on thecathode lead 8. This sleeve is made of a material which not onlypossesses the properties of good heat radiation but also has a high workfunction. Thus the sleeve 8a not only tends to keep the temperature ofthe lead 8 below its electron emission temperature but also covers saidconductor with a material which will not emit electrons even if thetemperature of the lead-in structure does rise, due to excessive loads,to comparatively high values.

Since it is the emission of electrons from the' lead-in conductors whichcauses the discharge to localize on them, the sleeve 8a by eliminatingsuch emission eflectively eliminates such localization of the discharge.

In order to provide a supply of vapor to said hollow cathode, I providethe spout arrangement immediately below the cathode 2, as shown in Figs.1 and 2. This spout arrangement is supported from a tubular extension 33formed integrally with the bottom wall of the envelope I. Within thistubular extension is provided an insulating plug 34, preferably of lava,held within the tubular extension by the side walls of said tubularextension being pressed into indentations in the sides of the insulatingplug 34 at points 35 and 36. The upper end of the insulating plug 34 isprovided with a circular recess in which is seated the combined spoutand shield 31. The bottom of the insulating block 34 is provided with aconcave recess 38 in the outer end of which is received a cup 39. Thiscup is retained in place by wires 54 projecting into holes in the block34 provided for that purpose. A longitudinal passage 40 extends throughthe insulating plug 34 from the upper to the lower recess. The combinedspout and shield 31 consists of an inner tubular member 4| having apartition 42 extending across said tubular member at a slight distanceabove its lower end. This partition 42 is provided with an opening 43 onone side of the center thereof. The tubular member 4| is approximatelycf the same size and diameter as the shield 28, and is positionedconcentric therewith in such a manner that the outer ends of said shield28 and tubular member 4| are at a short distance from each other. Thetubular member M is concentrically surrounded by a heat shielding member44 having a lower wall 45 joined to the lower end of tubular member 4|.The wall 45 has a central opening 46 registering with the upper end ofthe passage 40. The heat Shield 44 is contained within the circularrecess in the upper end of the insulating block 34, and may bemaintained in place thereon by some such means as a wire 41 fixed to thebottom wall 45, extending through the insulating block 34 and bent overonto the lower face of said block within the recess 38. The upper end ofthe heat shielding member 44 carries an enlarged shielding member 48which extends above the lower end of the shield 20 and completelysurrounds the cathode. This shield 48 may be provided with an offsetportion 49 at one side thereof in order to accommodate the ends l1 andI8 and the clamping bolts IS. The shield 48 is provided with a lowerwall 49 which is joined to the upper end of the shield 44. A fiatheat-shielding member 50 is connected to the outer wall of the shield 44and interposed between the wall 49 of the shield 48 and the adjacentwall of envelope I. It will be noted that although the discharge openingof the cathode is quite near the lower wall of the envelope I, yetbetween the cathode discharge opening and all portions of the wall ofthe envelope nearest said cathode opening there are interposed twospaced heat shields, while between the cathode discharge opening andthose portions of the wall which are farther away from said openingthere is interposed the single heat shield 48. Those portions of thewall of envelope I which are in line with the cathode discharge openingand have no interposed shield are so far away from said cathode thatthey are not unduly affected by the heat radiations emitted at saiddischarge opening. The heat shields not only protect the walls of theenvelope I, but also keep the heat liberated at the cathode within thecathode chamber, am. by the resultant increased thermal agitation of thevapor therein assist in the ionizing of the vapor, thus aiding inreducing the cathode drop.

The tubular extension 33 is adapted to be filled with a vaporizablematerial, such as, for example, mercury 380., which furnishes thedischarge supporting vapor and which normally fills the spoutarrangement to a level above the partition 42. The insulating block 34is provided with grooves which enable the condensed vapor to run backinto the lower end of the tubular extension 33.

Each of the anodes 3 and 4 is disposed transversely of the envelope l atright angles to the line of the cathode structure. Each anode consistsof a hollow elongated tubular member 55 composed of a conductingrefractory material having a very high work function, or at least a workfunction which is sufficiently high so that electrons are not readilyliberated even under conditions of fairly high temperature andbombardment by excited atoms. This material is preferably carbon. Theopposite ends of this tubular member 55 are supported by two reentrantstems 56 and 51, provided in tubular extensions 58 and 59 formedintegrally with the walls of the envelope l. The tubular member 55 issupported on these reentrant stems by means of plugs 60 and GI which arethreaded into the opposite ends of said tubular member 55. These plugsconsist preferably of insulating refractory material, such as lava,while if not of insulating material they also are formed of a materialhaving the requisite high work function. In the inner wall at the outerenlarged end of each of said plugs is provided an annular recess 62 inwhich is contained a coiled annular spring 63. The inner diameter ofeach of the plugs GI! and 6| is made so as to fit snugly around theouter diameter of the reentrant stems 56 and 51. The springs 63 take upany clearance which may exist between the plugs and the walls of thereentrant stems, and thus the anode structure is resiliently supportedat both ends thereof. Through the inner wall of one of the reentrantstems is sealed an anode lead 64, consisting of a heavy tungsten rod.This lead 64 is sealed through the wall of the reentrant stem by meansof a seal 65 similar to seal 9 referred to above. The outer end of therod 64 is also provided with a stranded copper conductor 66, wherebyconnections may be made to the external circuit. Around the inner end ofthe conductor 64 is clamped a laminated spring connecting member 61.This connecting member is clamped to the rod 64 by some suitableclamping arrangement, such as 68, consisting of clamping plates andbolts. The tubular member 55 is interiorly thickened to provide anannular ledge 69, and at diametrically opposite points on this ledge thetwo outer ends of the connecting member 61 are clamped to the tubularmember 55. This clamping arrangement is provided by bolts extendingthrough the walls of the tubular member 55 and the outer ends of theconnecting member 61, and being screw-threaded into clamping plates 1|mounted on the outer ends of said connecting member. Upon operation ofthe device, the temperature of the anode structure and of the walls ofenvelope i will increase. Since the coefficient of expansion of each ofthese members is different, motion must be permitted to occur betweenthese members if strains are to be avoided. It will be seen that theanode is free to move longitudinally with respect to the reentrant stems56 and 51, and also any resultant variation in the clearance between theplugs 60 and Bi and the stems 56 and 51 will be taken up by the springs63. The resilient connection between the anode and its lead-in conductorafiorded by the connecting member 61 permits relative motion between theanode and its lead-in conductor 64, and thus prevents any excessivestrain from occurring at the seal 65. It should also be noted thatsubstantially none of the weight of the anode is supported by the lead64 or seal 65, and thus this source of strain on the seal is alsoeliminated. This structure functions so that no strains are developedeven during large variations in temperature, and the anode is alwaysfirmly but resiliently supported on the stems 56 and 51.

The outer Walls of the tubular member 55 are countersunk to receive theheads of the clamping bolts 10. These counter-sinks are sufficientlydeep so that plugs 12 may be inserted therein to cover the heads of theclamping bolts. These plugs are also of the requisite high work functionmaterial, and are also preferably constructed of carbon. Upon inspectionof the anode structure, it will be seen that the portions of the anodeand of the members which are connected to the anode and which areexposed to the discharge vapor within the envelope I are composed solelyof a refractory material of a work function high enough to prevent theemission of electrons from said material, due either to hightemperatures or to collision therewith of excited gas atoms. When thesematerials are of carbon and of insulating material, such as lava, assuggested above, it will be seen that no metal parts whatsoever, whetherof the anode itself or of members connected to the anode, are exposed tothe discharge vapor within the envelope I.

As will be pointed out below, an activating agent, such as an alkalineearth or alkali metal is placed within container I. In the specificationand claims I use alkaline metal as a generic term to cover both alkaliand alkaline earth metals. The vapor of such metals has a strongtendency to settle on metal surfaces, making them good electron emittersat comparatively low temperatures. These activating materials have verylittle tendency to settle upon the materials of the anode structurewhich I have specified as being exposed to said vapors. While in knownstructures the introduction ofsuch activating materials would increasethe tendency for reverse currents to be drawn from the anode leadins andsimilar parts, yet due to the peculiar arrangement of my device, theintroduction of these materials does not materially diminish theproperty of my device to withstand high reverse voltages withoutappreciable reverse currents passing. The anodes 3 and l are located onopposite sides of the cathode, and since the cathode is placed adjacentthe lower wall of the envelope, the anodes can be placed at such a levelabove the discharge opening of the cathode that the line which connectsthe cathode discharge opening and each anode when projected intersectsthe wall of envelope I at the greatest possible distance from thecathode discharge opening. The arrangement affords an additional measureof protection for the walls of envelope I. In discharge devices of veryhigh power'and voltage rating, the bombardment of the walls of thedevice by high speed electrons and ions, may become so severe as toinjure the wall, particularly if it is made of glass. The shieldingstructure around and below the cathode effectively prevents suchbombardment of the wall of the envelope adjacent the cathode. Moreoverthe form of my device enables the maximum distance between the walls inline with the discharge, and the active portion of the cathode asdescribed above, to be suflicently long so 'that the rest of theenvelope wall is likewise protected against bombardment;

In order to maintain the pressure within the envelope I at its propervalue, I provide condensing chambers 13 and H. A large part of theenergy which is liberated in the device manifests itself as heatliberated adjacent the cathode. This heat, if allowed to be transmittedto the condensing chambers, would raise the temperature thereof. Alsothere is a considerable amount of other radiations liberated fromexcited atoms within the vapor. These radiations, if absorbed by thewalls of the condensing chambers would also raise the temperaturethereof. Thus it is necessary to remove these condensing chambers to apoint remote from the cathode itself so as to decrease the amount ofheat which is transmitted directly to these condensing chambers and alsoto provide means for shielding the walls of these chambers against theradiations referred to. The particular form of container which I useenables me to obtain sufliciently remote spac ing of these chambers fromthe cathode and the shielding of their walls from the radiations with noincrease in complexity of the device. This is accomplished by providingon the envelope I on its outer extremities of its longitudinaldimension, tubular extensions I5 and I6. In the upper walls of thesetubular extensions and 16 are formed the condensing chambers II and I4.It will be seen that each of these condensing chambers is removed as faras possible from the cathode itself, and their locations aresufllciently remote from the cathode so that the heat liberated theredoes not raise the temperature of these condensing chambers to anyconsiderable extent. It will be noted that the position of thesecondensing chambers also is such that the walls of the envelope I absorball radiations generated in the vapor within said envelope before theycan reach the condensing chambers. Thus these chambers are effectivelyshielded against these radiations and their temperatures are thereforenot ail'ected by said radiations. Thus the temperature of the condensingchambers will at all times be very slightly higher than that of thesurrounding space which under ordinary circumstances will be at theusual room temperatures. Since there is very little resistance to theflow of vapor from the interior of envelope I to the condensing chamber13, the vapor pressure in envelope I is substantially dependent upon thetemperature of its coolest portion. This pressure will be determined bythe temperature of the condensing chambers. By maintaining thesechambers at the temperatures indicated, the vapor pressure is keptwithin the desired limits. If it is desired, the chambers I3 and H canbe provided with additional cooling means, such as cooling coils and thelike.

The voltage drop through a vaporous atmosphere, such as, for example,mercury vapor, can be greatly decreased by providing a clean-up agentwhich cleans up or combines with the impurities which may be present.Some materials not only possess this property, but also increase theelectron-emitting properties of the cathode, or help to maintain theelectron-emitting properties thereof unimpaired throughout the life ofthe tube when deposited upon said cathode. I prefer to introduce amaterial which possesses all of the above properties, and have designedmy device particularly with a view to utilizing each of the aboveeffects. As my clean-up and activating agent I prefer to use an alkalior alkaline earth metal, and in the particular tube which I haveillustrated I utilize barium as said agent. The usual method ofintroducing a clean-up agent into a discharge tube is merely to vaporizethe clean-up material within the tube, and deposit it indiscriminatelyupon the walls of the container. If such a procedure is adopted in avapor discharge device, such as I have described, some clean-up will beeifected. However, it is desirable that this clean-up agent be activethroughout the life of the tube, and therefore It should be intimatelymixed or amalgamated with the vaporizable material in order that thismaterial shall constantly be kept clean by the cleanup agent. Theindiscriminate depositing of the clean-up agent on the walls of thetube, however, makes the mixing of the vaporizable material in theclean-up agent a very uncertain one, inasmuch as but a small amount ofthe vaporizable material ever comes into actual contact with theclean-up agent. In accordance with my invention, however, I provide aliberal supply of the clean-up agent in direct contact with the body ofvaporizable material. I place a mixture which upon heating liberates theclean-up and activating material within the cup 39 before said cup isinserted in place within the tube. This mixture is preferably one whichliberates an alkali or alkaline earth metal, such as, for example,barium.

The entire structure is then assembled, as shown in the drawings, exceptthat exhaust tubes are connected to the outer ends of each ofthecondensing chambers I3 and 14. The envelope is then thoroughlyevacuated, and all of the electrodes and other elements within theenvelope I are thoroughly freed of occluded gases in the usual manner,by heating and the like. However, during this process, the mixturewithin the cup 39 is not flashed. After the envelope isthoroughlyevacuated, the cup 39 is heated, as, for example, by inducinghigh frequency currents therein, and is raised to a sufficiently hightemperature to flash the mixture contained therein. Upon flashing, theclean-up and activating material which is liberated will deposit uponthe walls of the recess 38, the interior walls of the passage 40, andprobably also on the inside walls of the combined spout and shieldmember received in the upper recess of the insulating block 34. Aquantity of vaporizable material, such as mercury, is then introducedinto the envelope suflicient to fill the structure within the tubularextension 33 to a level above the partition 42. It will be noted thatthe walls upon which the clean-up and activating material has beendeposited are those walls upon which the mercury comes into direct andconstant contact. Thus the mercury is brought intimately into contactwith the clean-up agent. This intimate contact continues throughout thelife of the tube so that there is always a supply of clean-up agentdirectly available to absorb any impurities which enter the mercury. Theintimate contact between the mercury and barium produces an amalgam ormixture of these two materials. I wish it to be understood that the termmixture as used in the claims is to be construed in its broad sense ofmeaning the result of the admixture of two materials even if such amixture might also be termed an amalgam, alloy, solution, or the like.When such a mixture has vaporized and vapors. of both materials aregiven off, it is also proper to call such resultant vapors a mixture ofthe two materials.

Although materials, such as alkali and alkaline earth metals, whendeposited upon the cathode will improve its electron-emittingproperties, as indicated, yet when these materials are simply mixed withthe principal vaporizable material, it is diflicult to cause theactivating material to be deposited upon the cathode surface. This isprobably due to the fact that the vaporizing temperatures of theactivating agent and of the principal vaporizable material aredifferent. Although the vapor of the activating material may be detectedwithin the container along with the principal vapor, yet this amount isordinarily insufiicient to utilize to its fullest extent the activatingproperties of said agent. My arrangement, however, enables me to securethe direct deposition of particles of the activating agent upon thecathode surface. This is accomplished by disposing the active cathodesurface fairly close to the upper surface of the body of vaporizablematerial within the tubular member 4|. During the operation of the tube,the heat generated by the heating filament 22 and by the dischargepassing from the active cathode surfaces is substantially confinedwithin the shield 20 and the tubular member 4| by the surrounding heatshielding structure. The surface of the vaporizable material within thetubular member 4| is exposed directly to the heat so generated. As aresult, this vaporizable material is raised to a temperature at which itbegins to vaporize violently. The upper surface of the vaporizablematerial is consequently in a constant state of vigorous agitation,whereby small particles 11 are thrown off said surface. Since theseparticles are liberated by the mechanical motion of the surface, theycontain not only the vaporizable material but also a considerable amountof the activating agent. The degree of agitation of the surface of thevaporizable material is sufficient to cause a large number of theparticles so thrown off to come in contact with the cathodeelectronemitting surfaces. These surfaces appear to have a very strongailinity for the activating agent, and therefore the material comprisingthis agent is readily deposited upon the cathode surface. In this mannerthroughout the operation of the device, the cathode surface is beingconstantly renewed by a continuous deposition of the activating agentthereupon,

The spout arrangement below the cathode, in addition to the otherfunctions, operates to prevent the pressure within the cathode chamberfrom rising to too high a value. Since the pressure outside of thecathode is fairly constant as determined by the temperature of thecondensing chambers 13 and 14, upon an increase in pressure in thecathode chamber the surface of the vaporizable material in the tubularmember 4| will be depressed by said pressure. This depression has noappreciable effect until the pressure in the cathode chamber rises tosuch a value that the surface of the vaporizable material is depressedbelow the partition 42. When this occurs, the partition 42 acts as aheat shield between the heat generated ln the cathode chamber and thevaporizable material below said partition. Since the vaporizablematerial is evaporated solely by the heat furnished from the cathodechamber, no additional material is vaporized as long as the surface ofthe vaporizable material is below the partition 42. Since there is aconstant flow of vapor out through the oathode discharge opening intothe lower pressure region, upon the vaporization of the vaporizablematerial ceasing, the pressure within the oathode will drop until thesurface of the vaporizable material again rises above the partition 42.Thus the maximum pressure which can be reached within the cathodechamber can be controlled by properly designing the spout arrangement,particularly with respect to the location of the partition 42. Thehigher this partition is placed, the lower will be the maximum pressurewithin the cathode chamber, while the lower the partition is located,the higher will be the maximum pressure developed within said cathodechamber. Such an arrangement is a particularly simple and effectivepressure control.

It will be seen that the cathode is supported very close to the bottomwall of the envelope for various reasons as set forth above, such as,for example, to obtain a distant location of the envelope wall in thedirection of the discharge and to obtain close spacing between thecathode and the body of vaporizable material. Since the cathode shouldalso be supported from. the opposite wall to protect the seals and thelike, the length of the supporting stem lead-in and supporting wiresmight be excessively long with some shapes of envelopes. By making myenvelope longer in one direction than in another and disposing mycathode support across the shorter dimension, my cathode supportingstructure can be kept as short as possible. This shortening of thecathode supportingstructure can be obtained without decreasing theadvantages which follow as a result of the relative spacing of thevarious parts as set forth above.

The device described above may be connected in some suitable utilizationcircuit which may be, for example, such as that shown in Fig. 5. Atransformer 18 is provided with a primary 18 connected to a suitablesource of alternating current. This transformer carries a secondary 88to the opposite terminals of which are connected two anodes 3 and 4. Aconductor 8i is connected from the midpoint of the secondary 88 to oneend of an inductive choke 82, the other end of said choke beingconnected by means of a conductor 88 to one side of some suitable load84. The other side of said load 84 is connected by means of a conductor85 to the cathode 2. The heating filament 22 is energized by anauxiliary secondary 88 of the transformer 18. This secondary 88furnishes heating current to the filament 22 through conductors 81 and88. An additional secondary 89 is provided on the transformer I8. Aconductor 90 connects one end of this secondary to the conductor 85, theother end of said secondary 89 being connected through a resistance 8|and a conductor 92 to the conductor 81 of the heating filament 22. Uponenergizing the primary I8, the filament heating winding 86 heats thefilament 22 to incandescence, whereupon said filament not only startsheating the cathode electron-emitting surfaces, but also itself beginsto emit electrons. A potential difference is established between theheating filament 22 and the surrounding cathode structure by means ofthe winding 88. A discharge is therefore initiated between said filament22 and said surrounding cathode structure, which discharge is limited bythe resistance 8|. This discharge not only increases the heating effecton the surrounding cathode structure, but also causes some of theelectrons generated by said discharge to pass out through the openings82 provided in said surrounding cathode structure. Thus, very early inthe operation of the device, a large number of electrons appears atthese openings 82. The presence of these electrons assists in theimmediate starting of the discharge between the anodes and the cathode.Also the fact that the number of electrons adjacent these openings is inexcess of the number of electrons adjacent any other portion of thecathode surface tends to cause the discharge to concentrate at thesepoints rather than on some external surface of the cathode where such aconcentration would be objectionable. Upon the starting of the dischargebetween the anodes and the cathode, a direct current will flow throughthe load device 84. Although the amount of current which ordinarilypasses between the anodes and the cathode is so large that it mightinjure such a filament as 22, yet since this filament is entirelyenclosed within the hollow member II, it is not placed in the path ofthis main discharge and is consequently not affected by it. However,said filament continues to emit electrons and is therefore always readyto aid in initiating the main discharge if for any reason this dischargeshould be cut off at any time.

By constructing a device in accordance with the invention describedabove, I have been able to construct such a rectifier as shown which hasbeen able to rectify 300 amperes at volts with a drop of about 4 volts.However, it should be borne in mind that this is merely one embodimentof my invention, and that even better results can be obtained byconstructing devices in accordance with the invention herein described.

This invention is not limited to the particular details of construction,materials and processes described above. For example, certain featuresof my invention may be utilized with the anodes constructed of somesuitable refractory metal, such as, for example, iron, molybdenum, orthe like. Also instead of using mercury vapor as the gaseous atmospherewithin the tube, other vapors or gases, such as the vapors of alkalimetals or rare, monatomic gases, could be utilized. Various otherequivalents of these and other features of my .invention will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurate withthe scope of the invention within the art.

What is claimed is:

1. A gaseous discharge device comprising a hermetically sealed envelopecontaining a cathode, two anodes, and an atmosphere of an ionizablevapor, said envelope being considerably longer in one dimension than inanother, the active portion of said cathode being supported adjacent onewall of said envelope at substantially the central portion thereof, saidwall having as one of its dimensions said longer envelope dimension,said anodes being supported on opposite sides of said cathode, thelength of the line extending from the active portion of said cathode toeach of said anodes and extended to the wall of the envelope being amaximum for said envelope, and condensing chambers located at theopposite extremities of the longer dimension of said envelope.

2. A gaseous discharge device including a hermetically sealed envelopecontaining an anode, a cathode including a hollow chamber, means forsupplying an ionizable vapor to the interior of said hollow chamber, thepressure within said hollow chamber to be maintained higher than thepressure outside of said hollow chamber and within said envelope duringoperation of said device, and means responsive to the difference inpressure between the interior and exterior of said chamber to preventsaid difference from rising above a predetermined value.

3. A gaseous discharge device including a hermetically sealed envelopecontaining an anode, a cathode including a hollow chamber, means forsupplying an ionizable vapor to the interior of said hollow chamber,said means comprising a hollow member, a body of vaporizable materialwithin said hollow member and serving as the source of said vapor, meansfor supplying heat to the surface of said vaporizable material tovaporize said vaporizable material, the pressure within said hollowchamber to be maintained higher than the pressure outside of said hollowchamber and within said envelope during operation of said device, meansfor rendering the levelof the surface of said vaporizable materialinversely responsive to the difference in pressure between the interiorand exterior of said hollow chamber, and a heat shield at apredetermined level in said hollow member and interposed between saidheat supplying means and the surface of said vaporizable material whenthe level of said surface drops below said predetermined level, wherebythe said pressure difference is maintained below a predeterminedmaximum.

4. A gaseous discharge device comprising a hermetically sealed envelopecontaining an anode, an ionizable atmosphere, said anode being in theform of a hollow cylinder, said envelope having a reentrant stemprojecting into and substantially closing one end of said hollowcylinder, means for 7' ode outside of said hollow anode, said anodecom-.

pletely shielding said anode lead-in wire from exposure to theatmosphere within the discharge space in said envelope.

5. A gaseous discharge device comprising 'a hermetically sealed envelopecontaining an anode, said anode being in the form of a hollow cylinder,said envelope having two reentrant stems in line with one another inopposite walls of said envelope, said reentrant stems projecting intoopposite ends of said anode and supporting said anode, and a cathodeoutside of said hollow anode.

6. A gaseous discharge device comprising a hermetically sealed envelopecontaining a cathode, an anode, said anode being in the form of a hollowcylinder, said envelope having two reentrant stems in line with oneanother in opposite walls of said envelope, said reentrant stemsprojecting into opposite ends of said anode and supporting said anode, alead-in wire for said anode, said lead-in wire being sealed through oneof said stems within said hollow cylinder, said lead-in being connectedto said anode by a resilient conductive connector.

'7. The method of introducing vaporizable material and a vaporizableclean-up agent into a gaseous discharge tube comprising, firstevacuating the tube, then vaporizing said clean-up agent and depositingit from vapor phase upon selected surfaces within said tube and coveringsaid surfaces with said vaporizable material as it is introduced intosaid tube.

8. The method of introducing vaporizable material and an alkaline metalinto a gaseous discharge tube comprising first evacuating the tube, thenvaporizing said alkaline metal and deposit-- ing it from vapor phaseupon selected surfaces within said tube and covering said surfaces withsaid vaporizable material as it is introduced into said tube.

9. The method of introducing mercury and barium into a gaseous dischargetube comprising first evacuating the tube, then vaporizing said bariumand depositing it from vapor phase upon selected surfaces within saidtube and covering said surfaces with said mercury as it is introducedinto said tube.

10. The method of introducing vaporizable material and an alkaline metalinto a' gaseous discharge tube comprising placing said alkaline metal ata selected place within said tube, evacuating the tube, and coveringsaid place with said vaporizable material as it is introduced into saidtube.

11. The method of introducing mercury and barium into a gaseousdischarge tube comprising placing said barium at a selected place withinsaid tube, evacuating the tube, and covering said place with saidmercury as it is introduced into said tube.

12. A gaseous discharge device comprising a hermetically-sealed envelopecontaining a hollow cathode, an anode, an atmosphere of an ionizablevapor, a body of vaporizable material for supplying said vapor, means toconduct the vapor from said material to said hollow cathode, comprisinga hollow conduit extending from said body to said hollow cathode, and aheat shield around said conduit comprising a metal member surroundingand spaceda small distance from the outer walls of said conduit.

13. A gaseous discharge device comprising a hermetically-sealed envelopecontaining a hollow cathode, an anode, an atmosphere of an ionizablevapor, a body of vaporizable material for supplying said vapor, means toconduct the vapor from said material to said hollow cathode, comprisinga hollow conduit extending from said body to said hollow cathode, and aheat shield around said conduit comprising a wall member surrounding andspaced a small distance from the outer walls of said conduit.

14. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a solid, substantially non-vaporizabledischarge surface, a'body comprising a mixture of a vaporizable materialfor furnishing an ionizable vapor for supporting a discharge betweensaid discharge surface and said anode, and an activating material whichmaintains the electron-emitting qualities of said surface when conveyedthereto, said'body positioned in said vessel to prevent thedischargefrom emanating from said body during normal operation, and means forseparating from said body some of said vaporizable material and saidactivating material and conveying the materials so separated to saidsurface during operation.

15. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a solid, substantially non-vaporizabledischarge surface, a body comprising a mixture of a. vaporizablematerial for furnishing an ionizable 'vapor for supporting a dischargebetween said discharge surface and said anode, and an alkaline metal,said body positioned in said vessel to prevent the discharge fromemanating from said body during normal operation, and means forseparating from said body some of said vaporizable material and saidalkaline metal and conveying the materials so separated to said surfaceduring operation.

16. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a solid, substantially non-vaporizabledischarge surface, a body comprising a mixture of mercury for furnishingmercury vapor for supporting a discharge between said discharge surfaceand said anode, and barium, said body positioned in said vessel toprevent the discharge from emanating from said body during normaloperation, and means for separating from said body some of said mercuryand said barium and conveying the materials so separated to said surfaceduring operation.

17. A gaseous conduction device comprising a gas-tight vessel containingan anode, a thermionic cathode having a solid, substantiallynonvaporizable discharge surface, a body comprising a mixture of. avaporizable material for furnishing an ionizable vapor for supporting adischarge between said discharge surface and said anode, and anactivating material which maintains the electron-emitting qualities ofsaid surface when conveyed thereto, said body positioned in said vesselto prevent the discharge from emanating from said body during normaloperation, and means for separating from said body some of saidvaporizable material and said activating material and conveying thematerials so separated to said surface during operation.

18. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a discharge surface, separate heating meansfor heating said discharge surface to temperature of thermionic emissionduring operation, a body comprising a mixture of a vaporizable materialfor furnishing an ionizable vap'or for supporting a discharge betweensaid discharge surface and said anode, and an activating material whichmaintains the electron-emitting qualities of said surface when conveyedthereto, and means for separating from said body some of saidvaporizable material and said activating material and conveying thematerials so separated to said surface during operation.

19. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a solid, substantially non-vaporizabledischarge surface, a body comprising a mixture of a vaporizable'materialfor furnishing an ionizable vapor for supporting a discharge betweensaid discharge surface and said anode, and an activating material whichmaintains the electron-emitting qualities of said surface when conveyedthereto, said body positioned in said vessel to prevent the dischargefrom emanating from said body during normal operation, and means forvaporizing material from saidbody and conveying the material thusseparated from said body to said surface during operation.

20. A gaseous conduction device comprising-a gas-tight vessel containingan anode, a cathode having a solid, substantially non-vaporizabledischarge surface, a body comprising a mixture of a vaporizable materialfor furnishing an ionizable vapor for supporting a discharge betweensaid discharge surface and said anode, and an activating material whichmaintains the electronemitting qualities of said surface when conveyedthereto, said body positioned in said .vessel to prevent the dischargefrom emanating from said body during normal operation, means forvaporizing material from said body and conveying the material thusseparated from said body to said surface during operation, and means forcondensing the vapor in said vessel and returning said condensed vaporto said body.

' 21. A gaseous conduction device comprising a gas-tight vesselcontaining an anode, a cathode having a discharge surface, said surface.being provided with a coating of electron-emissive oxide, a bodycomprising an activating material which maintains the electron-emittingqualities of said surface when conveyed thereto, and means forseparating from said body some of said activating material andconveyingthe material so separated to said surface during operation.

22. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a discharge surface, said, surface beingprovided with a coating of electron-emissive oxide, a body comprising analkaline metal, and means for separating from said body some of saidalkaline metal and conveying the materials so,

separated to said surface during operation.

23. A gaseous conduction device comprising a gas-tight vessel/containingan anode, a cathode having a disc arge surface, said surface beingprovided with a coating of oxide, a body comprising an alkaline metal,and means for separating from said body some of said alkaline metal andconveying the materials so separated to said surface during operation.

24. A gaseous conduction device comprising a gas-tight vessel containingan anode, a cathode having a discharge surface, said surface beingprovided with a coating having a high aiiinity for alkaline metal, abody comprising a. mixture of a vaporizable material for furnishing anionizable vapor for supporting a discharge between said dischargesurface and said anode, and an alkaline metal, and means for separatingfrom said body some of said alkaline metal and conveying the materialsso separated to said surface during operation.

25. A gaseous conduction device comprising a gas-tight vesselcontainingan anode, a hollow cathode having an interior solid,substantially non-vaporlzable discharge surface and a discharge opening,a body comprising a mixture of a vaporizable material for furnishing anionizable vapor for supporting a discharge between said dischargesurface and said anode, and an activating material which maintains theelectron-emitting qualities of said surface when conveyed thereto, saidbody positioned in said vessel to prevent the discharge from emanatingfrom said body during normal operation, means for separating from saidbody some of said vaporizable material and said activating materialduring operation, and a conduit extending from said body to the interiorof said hollow cathode for conveying the material so separated to saidsurface.

26. A' gaseous conduction device comprising a gas-tight vesselcontaining an anode, a hollow cathode having an interior solid,substantially non-vaporizable discharge surface and a restricteddischarge opening maintaining a higher pressure inside said hollowcathode than outside said cathode, a body comprising a mixture of avaporizable material for furnishing an ionizable vapor for supporting adischarge between said discharge surface and said anode, and anactivating material which maintains the electron-emitting qualities ofsaidsurface when conveyed thereto, said body positioned in said ,vesselto prevent the discharge from emanating from said body during normaloperation, means for vaporizing material from said body and conveyingthe material thus separated from said body to said surface duringoperation comprising a conduit extending from said body to the interiorof said hollow cathode, and means for condensing the vapor in saidvessel and returning said condensed vapor to said body.

27. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface which comprises conveying to the electron-emissive surface ofthe cathode during operation a mixture of an easily vaporizable materialand a material which maintains the electronemitting-properties of saidsurface.

28. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface which comprises conveying to the electron-emissive surface ofthe cathode during operation a mixture of an easily vaporizablematerialand an alkaline metal.

29. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface which comprises conveying to the electron-emissive surface ofthe cathode during optron-emissive oxide which comprises'conveying tothe electron-emissive surface of the cathode during operation a materialwhich maintains the electron-emitting properties of said surface.

31. The method of preserving the electronemitting properties of acathode coated with electron-emissive oxide which comprises conveying tothe electron-emissive surface of the cathode during operation a mixtureof an easily vaporizable material and an alkaline metal.

32. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface in a gas-tight vessel which comprises separating material from abody of a mixture of an easily vaporizable material and a material whichmaintains the electron-emitting properties of said surface, andconveying the materials so separated from said body to said surfaceduring operation.

33. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface in a gas-tight vessel which comprises separating material from abody of a mixture of an easily vaporizable material and an alkalinemetal, and conveying the materials so separated from said body to saidsurface during operation.

34. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface in a gas-tight vessel which comprises vaporizing material from abody of a mixture of an easily vaporizable material and a material whichmaintains the electron-emitting properties of said surface, andconveying the materials so separated from said body to said surfaceduring operation.

35. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface in a gas-tight vessel which comprises vaporizing material from abody of a mixture of an easily vaporizable material and a material whichmaintains the electron-emitting properties of said surface, conveyingthe materials so separated from said body to said surface duringoperation, condensing the vapor in said vessel, and returning thecondensed vapor to said body.

36. The method of preserving the electronemitting properties of acathode having a solid, substantially non-vaporizable electron-emissivesurface in a gas-tight vessel which comprises vaporizing material from abody of a mixture of an easily vaporizable material and an alkalinemetal, conveying the materials so separated from said body to saidsurface during operation, condensing the vapor in said vessel, andreturning the condensed vapor to said body.

LAURENCE K. MARSHALL.

